An important point to remember is that if you shoot through the door at an unknown target of unknown danger then you are liable. Forget the "judged by 12/carried by 6" stuff. If you shoot at someone who is not threatening you (or another person) then you will go to jail. And you may kill someone who is completely innocent. There are a hundred reasons why someone may be rattling your door knob. Being scared isn't a reason to take a life.
-Don’t get me wrong- if someone walks in your door threatening your life then you would be justified to shoot them. But you had better be sure of your target. It might be the Cop who found your door open (after scaring off a burglar) and is checking the house for more burglars! It happens more than you think.
The short answer? Only a fool shoots at something he can't see!